Immunological correlation between morphine tolerance and the effect of naloxone in rats of different age

Abstract

In 3–6-week-old morphine-sensitive rats, in which morphine injection produced an analgetic effect, the serum titer of antimorphine antibodies 24 h postinjection is less than half that observed in morphine-resistant animals. Administration of naloxone to morphine-sensitive rats induces hyperalgesia and considerably raises the serum titer of antimorphine antibodies. Chronic injections of the same dose of morphine, which cause its analgetic effect to disappear, increase the titer of antibodies in morphine-sensitive rats 2-fold. In morphine-resistant rats naloxone produces an analgetic effect followed by its gradual decay and disappearance in the course of chronic administration. Subsequent administration of morphine induces analgesia, raises the titer of antimorphine antibodies, and lowers the titer of antiidiotypic antibodies.